Ruby threads and processes fun. Creating new thread, then forking off a child inside it and waiting for the child to finish. It works when using fork with a block argument, and it works when not creating a thread. But it doesn't work (hangs) when creating a thread and using fork with if/else syntax.

1-good.rb

t = Thread.new do
  pid = fork do
    puts "I'm the child #{Process.pid}"
    raise 'hello'
  end
  puts "Thread #{Thread.current.inspect}, pid: #{pid.inspect}"

  puts "I'm the parent #{Process.pid}"
  Process.waitpid(pid)
end

t.join

2-good.rb

# t = Thread.new do
  pid = fork
  puts "Thread #{Thread.current.inspect}, pid: #{pid.inspect}"

  if pid
    puts "I'm the parent #{Process.pid}"
    Process.waitpid(pid)
  else
    puts "I'm the child #{Process.pid}"
    raise 'hello'
  end
# end

# t.join

3-bad.rb

t = Thread.new do
  pid = fork
  puts "Thread #{Thread.current.inspect}, pid: #{pid.inspect}"

  if pid
    puts "I'm the parent #{Process.pid}"
    Process.waitpid(pid)
  else
    puts "I'm the child #{Process.pid}"
    raise 'hello'
  end
end

t.join